Method for depositing a reflective layer on glass, and products obtained

ABSTRACT

The subject of the invention is a process for depositing, especially continuously, on a glass ribbon (10) of a float line, a reflective layer (3) based on a metal whose melting point is less than or equal to the temperature at which the glass ribbon acquires dimensional stability. The deposition is carried out in a controlled atmosphere, this being inert or reducing, when the glass ribbon (10) has already acquired its dimensional stability, by bringing the surface of the said ribbon into contact with the metal (22) in pulverulent form or in molten form, the temperature of the ribbon during contacting being chosen so that the powder melts and coalesces, or so that the molten metal forms a sheet, at the surface of the ribbon, leaving a solid continuous layer when the temperature of the ribbon is at a temperature of less than or equal to the melting point of the metal.

The invention relates to the process of depositing a reflective layer,more particularly a metallic layer, on glass.

Depending on its thickness, a metallic layer may in fact impart variousproperties to a glass substrate intended to become a glazing panel: atrelatively low thickness, this metallic layer acts as a coating forprotection against solar radiation and/or as a low-emissivity coating.With a greater thickness, it enables a true mirror, having a very highlight reflectance, to be obtained.

The most widespread example is silver: it is known to deposit it as athin film, especially having an interferential thickness, using vacuumtechniques of the sputtering type, or as a thicker layer in order tomake mirrors, for example using the conventional wet technique of asilvering line. However, silver is a material of limited durability as athin film when it is exposed to a chemically aggressive medium, and thedeposition techniques mentioned above can only be carried out in asubsequent step, discontinuously, on glass plates once they have beencut from the glass ribbon of a float production line.

It is therefore worthwhile considering other metals, which haveproperties similar to silver but which could possibly be deposited,continuously and less expensively, directly on the glass ribbon of afloat line, and which have superior durability, for example aluminium.

It is thus known from Patent FR-2,011,563 to deposit an aluminium layeron a glass ribbon, when it is in the very chamber of the float bath,using a mass of molten metal emitting aluminium vapour towards theglass, the vapour condensing on the surface of the glass ribbon in orderto leave a continuous coating. However, this type of technique hasdrawbacks--it is tricky to implement, it is not easy to ensure adeposition of uniform thickness and, above all, the deposition rate islow, the limiting factor being the very low partial vapour pressure ofmetallic aluminium.

It is also known, from Patent GB-A-2,248,853, to deposit aluminiumlayers on a ribbon of float glass at a temperature of at least 100° C.Here, the technique used is one of pyrolysis in the liquid phase, inwhich organometallic compounds in a solvent are sprayed towards theglass and decompose into elemental metal on coming into contacttherewith. This type of pyrolysis is not devoid of drawbacks either--inparticular, it requires the discharging and treatment of largequantities of solvents.

The aim of the invention is then to develop a novel process forcontinuously manufacturing a metallic reflective layer on a ribbon offloat glass which palliates the aforementioned drawbacks and whichespecially makes it possible to obtain layers of high quality compatiblewith the requirements of the industrial production of glazing panels.

The subject of the invention is a process for depositing, especiallycontinuously, on a glass ribbon of a float line, a reflective layerbased on a metal whose melting point is less than or equal to thetemperature at which the glass ribbon acquires dimensional stability. Itconsists in carrying out the deposition in a controlled atmosphere, thisbeing inert or reducing, when the glass ribbon has already acquired thisdimensional stability, by bringing the surface of the ribbon intocontact with the metal in question in pulverulent form or in moltenform, the temperature of the ribbon during contacting being chosen sothat the powder melts and coalesces, or so that the molten metal forms asheet, at the surface of the ribbon, leaving a solid continuous layerwhen the temperature of the ribbon decreases during the flat-glassforming process down to a temperature of less than or equal to themelting point of the metal.

Within the context of the invention, "metal" is understood to mean amaterial having an electrical behaviour which is essentially of theconductive type. It is an essentially metallic material, either based onat least two metals, for example in the form of an intermetalliccompound, an alloy or a eutectic compound.

Advantageously, the "metal" according to the invention is based on atleast one of the materials belonging to the group comprising aluminium,zinc, tin and cadmium. Optionally, it may also comprise silicon oranother metal (especially in a concentration of less than 15 at. %).

As preferred non-limiting embodiments of this material, mention may bemade of aluminium, aluminiumtin alloys, aluminium-zinc alloys,aluminium-silicon compounds and, especially, the aluminium-siliconeutectic compound comprising 12 at. % of silicon and having a meltingpoint of approximately 575° C.

In addition, "continuous" layer is understood to mean a layer which canbe deposited on the glass ribbon so as to cover most, if not all, of itssurface. However, this also includes the layers which are deposited, forexample, in the form of parallel strips, and which therefore onlypartially cover, in an intentional and desired manner, the surface ofthe glass, for example for decorative purposes.

This also includes the layers which appear macroscopically continuousbut which, on a microscopic scale, may cover only part of the glassribbon.

Still within the context of the invention, "surface of the ribbon" isunderstood to mean not only the surface of the bare glass but also thesurface of the glass optionally treated/covered beforehand with at leastone given coating.

The invention preferably applies to a glass ribbon of a float line.However, it goes without saying that it is not limited thereto and thatit can also apply to a glass ribbon which might not come from a floatline or to a non-continuous glass substrate, such as a glass plate.

The process according to the invention has many advantages: on the onehand, within the invention the metal is used only in the solid phase orthe liquid phase, and not in the gas phase as in the aforementionedPatent FR-2,011,563. Consequently, the implementation of the process isgreatly facilitated since it is easier to control the distribution of apowder or a liquid than a vapour at the surface of the glass.Furthermore, this gets round the problem of the limiting factorconsisting of the vapour pressure of the metal, and it is thereforepossible to achieve markedly higher deposition rates. This is a keyadvantage for manufacturing layers having relatively large thicknesses,especially thicknesses sufficient to transform the glass into a mirror.This is because, in deposition operations on a float line in thefloat-bath chamber, the space in which the deposition may be carriedout, knowing that the glass must furthermore already be dimensionallystabilized, is quite small and it is therefore not necessarily possibleto "compensate" for the lower deposition rates by longer depositiontimes or longer metal/glass contacting times.

Moreover, the process according to the invention involves either anoperation of melting a metal powder or an operation of "sheeting" apremelted metal on the surface of the glass. There is therefore nopyrolysis in the usual meaning of the term, whether this is in the solidor liquid phase or in the gas phase (in this case, also known by theterm CVD or Chemical Vapour Deposition). This is because, on thecontrary, pyrolysis involves a chemical reaction step of thedecomposition of precursors of the organometallic-derivative type oncontact with the hot glass.

This difference has a very positive effect on the properties of thelayers obtained. The layers according to the invention have a tendencyto be more adherent, denser and less "rough" than pyrolysed layersbecause of the fact that they arise from the melting of an elementalmetal. They also have a tendency to crystallize better since, in theinvention, the crystallization takes place during the solidification ofthe layer at the rate corresponding to the cooling rate of the glassribbon along its path in the float line. The at least partialcrystallization of a pyrolysed layer generally takes place much more"abruptly", during decomposition of the precursors, and is oftenaccompanied by mechanical stresses.

The layers according to the invention also have a tendency to be purer,since there is little risk of impurities being incorporated into thelayers during formation, something which is not the case with pyrolysedlayers which may, for example, contain a certain amount of residualcarbon coming from the decomposition of organic precursors at the glass.

In addition, all these improvements lead to layers having higher qualityand greater durability: the denser the layer and the more adherent it isto the glass, the greater is its ability to resist corrosion, especiallyin a wet medium, or to resist oxidation, this being an advantage if theglass ribbon is subsequently cut into substrates intended to undergoheat treatments, such as a bending operation and/or a temperingoperation. A low surface roughness also ensures better corrosionresistance and minimizes any "haze" effect due to a certain amount ofdiffuse reflection. Finally, greater purity, especially a very lowamount of absorbent particles of the carbon type, associated with arelatively high degree of crystallization, gives the layers according tothe invention a very high light reflectance, something which is desiredabove all else in manufacturing mirrors.

The industrial feasibility of the process according to the inventiontherefore does not work to the detriment of the performance of thereflective layers thus manufactured, quite the contrary.

It is important that the depositions be carried out in an inert orreducing atmosphere, so as to ensure that there is oxidation neither ofthe metal powder before it comes into contact with the glass ribbon norof the layer itself while it is being formed. The deposition may becarried out in the float-bath chamber and thus take advantage of itscontrolled atmosphere, which is a mixture of nitrogen and hydrogen.Alternatively, it is possible to carry out the deposition downstream ofthe float-bath chamber, especially in an essentially sealed boxoptionally extending the said chamber. Such an "extension" is describedin particular in Patent FR-2,348,894.

Advantageously, the deposition of the reflective layer is carried outwhen the glass ribbon is at a temperature greater than or equal to themelting point of the metal: this thus ensures that the metal particlesreaching the glass do melt and/or that the molten metal is welldistributed at its surface.

The metal in pulverulent form may be brought into contact with thesurface of the glass in two different embodiments.

The first embodiment consists in spraying the said metal powder insuspension in a carrier gas, this being inert or reducing, in order toprevent it from oxidizing, especially using a distributing nozzle. Thismay be a static nozzle, which is arranged above the glass andsubstantially transversely to its running axis, over all or part of thewidth of the said ribbon. It may also be a moving nozzle, which is givena to-and-fro motion along an axis substantially transverse to therunning axis of the glass ribbon. In the case of depositing a layer madeof a single metal, for example Al, the powder is made only of particlesof the said metal. When the final layer is an alloy, the powder ispreferably a mixture of powders of each of the components in the finalcoating, it being possible to adjust the proportions of the mixture asrequired, or a powder directly produced from the alloy.

The particle size of the powder or of the mixture of powders (in factthe average diameter of the particles of which it is composed) isadvantageously between 0.1 μm and 100 μm and especially between 1.0 and50 micrometres, for example between 5 and 10 micrometres. In such aparticle-size range, the powder "particles" will be able to melt andcoalesce on the glass in an optimal manner.

The second embodiment consists in generating the metal, in pulverulentform above the glass ribbon, "in situ" from at least one metalderivative, especially a gaseous one, the decomposition of which into ametal is brought about by thermal activation and/or by bringingderivatives capable of reacting together into contact with each other.This is another way of ensuring that the metal, formed in the inert orreducing atmosphere existing above the glass, is not oxidized.Furthermore, starting from raw materials in gas form, it is possible touse the chemical vapour deposition (CVD) technology without having allthe aforementioned drawbacks thereof since, within the context of theinvention, if there is any decomposition it takes place above the glassand not on contact with it.

The powder thus formed preferably has the same particle size as thatmentioned previously.

Preferably, the metal powder is formed "in situ" from a metal derivative(or derivatives) chosen from metal alkyls, metal hydrides or mixed metalhydride/metal alkyl compounds complexed by ammonia or by an amine,especially alanes in the case of aluminium: either a single type of"precursor" is chosen or various types of precursors are chosen,especially when the layer to be obtained is made of an alloy.

Their temperature of decomposition into metal is generally between 50°C. and 600° C., especially between 100° C. and 450° C. It is thereforefound that such a temperature range does not coincide with thetemperature that the glass ribbon has during deposition of the layer:unlike chemical vapour deposition, there is a decorrelation between thedecomposition temperature of the chosen metal derivative and thetemperature of the glass at the time of deposition, and there istherefore much more freedom to optimize each of them independently ofthe other and to select the suitable metal derivative(s).

It is possible, within the invention, to combine with the metalderivative(s) at least one additive which promotes controlled nucleationor growth of the metal particles. This additive helps to adjust theparticle size of the powder formed above the glass.

The metal derivatives are therefore introduced above the glass ribbon ingaseous form, advantageously using a device whose walls define a channelfor guiding the powder generated. The walls of this cavity arepreferably substantially vertical, possibly divergent or, on thecontrary convergent towards the glass ribbon, and over at least part ofits height a suitable "thermal gradient" is created. By "thermalgradient" is meant a precise control of the temperature which, in arelatively gradual manner is preferably chosen so as to increase towardsthe glass. Adjusting this temperature gradient gives control of themoment when and the region in the cavity where, on the one hand, thedecomposition of the metal derivatives into metal particles takes placeand, on the other hand, good growth of the metal particles occurs inorder to reach a satisfactory particle size, in particular from 5 to 10micrometres as in the first embodiment according to the invention.

In a preferred variant, the process consists in injecting the metalderivatives in the upper part of the cavity of the device and inextracting the effluents arising from their decomposition by sideevacuation means made in the walls of the cavity, extraction preferablytaking place at the level, or near the level, where the metal powder isformed and where it reaches a sufficient particle size. In this way, itis ensured that they are evacuated before they touch the glass or areincorporated by chemical reaction into the metal particles in order toform, for example, a carbide or a nitride of the metal in question, thepowder itself "falling" simply under gravity onto the glass. Provisionmay also be made to inject, at at least one point in the cavity, aninert or reducing gas: this may help to avoid any risk of the metalpowder agglomerating on the walls of the cavity.

Moreover, since the cavity is at least partially in the inert and/orreducing atmosphere existing above the glass, it is itself designed soas to be filled with such an atmosphere. If the gaseous metalderivatives are introduced as a suspension in a carrier gas, the latterwill of course also be chosen preferably to have an inert and/orreducing nature.

Whether the metal powder is sprayed directly or using metal derivatives,it is necessary to understand in the invention that it liquefies orfuses either in contact with the glass or in the vicinity of the glass,but slightly above it, under the effect of the heat emitted at a shortdistance by the glass ribbon. The powder can therefore land on the glassin the form of a shower of droplets.

Another possibility according to the invention is to start not with ametal powder or gaseous metal derivatives, but with already molten metalwhich may be distributed on the surface of the glass using a staticdistributing nozzle arranged above the glass and transversely to itsrunning axis, which delivers a "curtain" of molten metal onto the glass.Alternatively, it is also possible to use a moving nozzle, given atransverse to-and-fro movement above the glass, of the spray-gun type.

As mentioned previously, the reflective layers according to theinvention have two highly advantageous properties:

on the one hand, they are dense, more so than layers which, for example,would be obtained by pyrolysis or, a fortiori, by vacuum depositiontechniques of the sputtering or evaporation type. This density,especially for aluminium layers, is at least 80 and even at least from90 to 95% of the theoretical density of the said material. Moreover,such a high density enables greater light reflectances to be achievedfor a given thickness (it should be noted that these densities may bemeasured, indirectly, using the electron densities measured by an X-rayreflectometer);

on the other hand, these layers contain no or very few impurities,carbon-, oxygen- or nitrogen-type impurities having a tendency toincrease the absorption and/or transmission of the layer to thedetriment of its light reflectance. This low amount of impurities istherefore matched in a high density, in order to achieve a maximummirror effect for a given thickness. The maximum impurity levels varyslightly depending on which process according to the invention ischosen: if one "starts" from materials, which will make up the layer, inpulverulent or molten form, without involving decomposition of at leastpartly organic precursors, the layer may be extremely pure. Thus, itgenerally contains only at most 1 at. % of impurities such as O or C,impurities which possibly become incorporated into the layer while it isbeing formed, for example by atmospheric pollution or being present inthe starting powder. Usually, the amount of impurities is less than 1at. % and remains below the detectability threshold of the measuringapparatus, in this case a scanning electron microprobe. In contrast, ifone starts with precursors in the form of at least partly organic metalderivatives, the reflective layers remain very pure, but possibly withan amount of impurities slightly above that in the previous case,especially at most from 2 to 3 at. %. These may be carbon, oxygen ornitrogen, especially when starting with alane-type compounds.

Whatever the manner in which the metal is brought into contact with theglass, it may be advantageous to treat the surface of the glass beforedepositing the metallic layer proper. There may be at least two reasonsfor carrying out such a pretreatment: on the one hand, it may beintended to facilitate wetting/bonding of the layer to the glass. On theother hand, it may also be intended to inhibit a spurious reaction atthe glass/metal interface which would tend to form, from the metal andthe silicon oxide contained in the glass, the metal oxide correspondingto the metal and silicon.

It may only be a surface "sensitization", consisting in bringing agaseous product in contact with the glass without there being a truechemical reaction, but with at least partial adsorption of the gas bythe surface of the glass. The gas may, for example, be titaniumtetrachloride TiCl₄.

However, the pretreatment may also comprise depositing at least oneso-called "interlayer" prior to the deposition of the layer. Theinterlayer or interlayers may advantageously be chosen based on at leastone of the materials belonging to the following group: silicon, oxidessuch as silicon oxide, oxycarbide or oxynitride, titanium oxide TiO₂,cerium oxide, aluminium oxide Al₂ O₃, zirconium oxide ZrO₂, zinc oxideZnO, nitrides such as aluminium nitride AlN, silicon nitride Si₃ N₄,titanium nitride TiN, zirconium nitride, boron oxide, yttrium oxide,magnesium oxide, mixed oxide of Al and of Si, fluorinated aluminiumoxide and magnesium fluoride MgF₂. It may also involve carbides. Theirdeposition is preferably carried out by chemical vapour deposition(CVD). This interlayer preferably has a maximum refractive index of 1.8and a light absorption at most equal to 3%. Its optical thickness may bebetween 40 and 120 nm and preferably between 70 and 100 nm. The chemicalrole of this interlayer is therefore the protection of the thin metallicreflective layer, either after production of the mirror, on leaving thefloat-bath chamber, or later during a subsequent heat treatment of themirror, or even over time, during the lifetime of the mirror undernormal use, for example in a bathroom.

Once the reflective metallic layer has been deposited on the ribbon offloat glass, it is recommended to envisage a post-treatment intended topreserve it from oxidation. The most effective way of doing this is tocover it with at least one so-called "additional" layer, especially whenthe ribbon is still in the inert or reducing atmosphere in which thedeposition of the reflective layer was carried out.

The additional layer or layers may in particular be chosen based on anitride, such as aluminium nitride, silicon nitride or titanium nitride.

However, they may also be based on an oxide (or oxides), especiallycomprising at least one oxide belonging to the following group: titaniumoxide TiO₂, tin oxide SnO₂, zirconium oxide ZrO₂, zinc oxide, niobiumoxide, tungsten oxide, antimony oxide, bismuth oxide, tantalum oxide oryttrium oxide, made of aluminium nitride or silicon nitride, orfluorinated tin oxide or made of diamond-like carbon (DLC) aluminiumoxide Al₂ O₃, made of silicon oxide, oxycarbide and/or oxynitride, orvanadium oxide. In the latter case, in order to further limit anycontact of the reflective metallic layer with an oxygen-containingcompound, provision may be made to deposit between the metallic layerand the oxide layer or layers a "sacrificial" silicon layer which issufficient to avoid metal/oxide contact but thin enough not to penalizethe stacking of layers in terms of light absorption (this comment alsoapplies when an "interlayer" made of pure silicon is chosen: it isadvantageous also to limit its thickness to a few nanometres). Thedepositions of the additional layer(s) are preferably carried out bychemical vapour deposition.

The additional layer covering the reflective metallic layer may have achemical composition gradient and/or a refractive index gradient throughits thickness. This may be an increasing or decreasing index gradient,especially by depositing a material having a low refractive index, (forexample lying between 1.45 and 1.60), which, while the layer is beingformed, becomes gradually richer in a material having a higherrefractive index, especially greater than 2, or vice versa. A chemicalcomposition gradient very advantageously enables two properties to beconferred on a single layer, and to optimize them in parallel withoutsacrificing one to the benefit of the other, especially as regards theadhesion of the layer to the layer (or layers) with which it is incontact, as well as its mechanical/chemical durability, etc.

This index gradient and/or this chemical composition gradient may beobtained by chemical vapour deposition by using a distributing nozzlehaving two injection slots, one for each gaseous precursor necessary forobtaining the two, low-index and high-index, materials, and byconfiguring it so as to cause, along the glass, partial and gradualmixing between the two gas streams emanating from two injection slots.

As the preferred "additional layer having a composition gradient", alayer based on silicon oxide is used which becomes gradually richer intitanium oxide: if a thin layer of "sacrificial" silicon is deposited onthe reflective layer, excellent Si/SiO₂ or Si/SiO_(x) C_(y) adhesion onthe reflective layer side is obtained, and the stacking is "completed"by titanium oxide which, if it is well crystallized, exhibits verybeneficial anti-fouling and/or anti-misting characteristics, apart fromits known photocatalytic properties.

It is also possible to choose to cover the metallic reflective layerwith at least one sequence of layers having high and low indices, forexample a SiO₂ /TiO₂ sequence.

Each additional layer preferably has a geometric thickness of at least10 nm, and especially lying between 20 and 150 nm, in particular between50 and 120 nm.

More generally, with regard to the nature of the materials making up the"external" complementary interlayers and "internal" additional layers,these are chosen so as to "interfere" optically with the reflectivelayer as little as possible.

Preferably, they are therefore chosen to be based on a material or amixture of materials which is (are) transparent in the wavelengths lyingwithin the visible.

They may thus be based on oxide(s), oxycarbide(s) or oxynitride(s) ofthe elements in Groups IIA, IIIB, IVB, IIIA and IVA and of thelanthanides in the Periodic Table, especially the oxides, oxycarbides oroxynitrides of magnesium Mg, of calcium Ca, of yttrium Y, of titaniumTi, of zirconium Zr, of hafnium Hf, of cerium Ce (CeO₂ or Ce₂ O₃), ofaluminium Al, of silicon Si or of tin Sn. As transparent oxides, it isalso possible to use doped metal oxides, such as fluorine-doped tinoxide F:SnO₂.

Among all these compounds, it is advantageous to choose oxides whichhave a standard free enthalpy of formation ΔG° per mole of oxygen athigh temperature, especially around 500 to 600° C., which is less thanor equal to that of the metal of which the reflective layer is made,referring for example to the diagram mentioning the free enthalpies offormation of oxides as a function of temperature, also known as theEllingham diagram. Thus, the oxidation of the metal of the reflectivelayer is thermodynamically not favoured and therefore any risk ofoxidation or of deterioration of the reflective layer when hot, duringits deposition which, if it is carried out on the ribbon of float glass,actually takes place in the region of from 450 to 700° C., is limited asfar as possible.

Thus, when the reflective layer is chosen to be based on aluminium, itis advantageous to choose, as external and/or internal complementarylayers, layers based on aluminium oxide, zirconium oxide, magnesiumoxide or lanthanum oxide. These oxide layers may especially be depositedusing solid-phase or liquid-phase pyrolysis techniques or chemicalvapour deposition. If the deposition is carried out in the float-bathchamber, it will more likely be chemical vapour deposition, CVD. Outsidethe float chamber, CVD, solid-phase pyrolysis or liquid-phase pyrolysistechniques may be used. Thus, it is possible by CVD to deposit layers ofoxide such as silicon oxide or silicon oxycarbide from gaseousprecursors of the silane and ethylene type, as described in PatentEP-0,518,755. The TiO₂ layers may be deposited by CVD from an alkoxide,such as titanium tetraisopropylate, and tin oxide, still by CVD, frombutyltin trichloride or dibutyltin diacetate. The aluminium oxide layersmay be deposited by liquid-phase pyrolysis or chemical vapour depositionfrom organometallic precursors such as aluminium acetylacetonate orhexafluoroacetonate.

The transparent complementary layers may also be chosen to be based on anitride or mixture of nitrides of at least one of the elements in GroupIIIA of the Periodic Table, such as aluminium nitride AlN, galliumnitride GaN_(x) or boron nitride BN_(x). The AlN layers may bedeposited, for example, by CVD, in a known manner, from aluminium alkylor hydride precursors combined with nitrogen-containing precursors ofthe ammonia and/or amine type. As the transparent nitride, siliconnitride Si₃ N₄ may also be used. This is because silicon nitride Si₃ N₄is also a very effective material for protecting the reflective layerfrom oxidation. It may be deposited by CVD from silane and ammoniaand/or an amine.

At least one of the complementary layers, and more particularly theexternal layer, may also be chosen to be based on a transparent materialof the diamond or diamond-like carbon (DLC) type, this type of materialhaving a high hardness and thus very effectively protecting thesubjacent stack of layers from mechanical abrasion, should this provenecessary (this is also true, to a lesser extent, in respect of titaniumoxide).

At least one of the "internal" and "external" complementary layers mayalso be chosen to be based not on materials which are transparent in thevisible but, on the contrary, based on material(s) which absorb to agreater or lesser extent in the visible, this or these materials beingdifferent from those which may moreover make up the reflective layer. Inorder that they do not interfere optically, or not to all intents andpurposes, as is the case with the transparent materials listed above, itis then preferable to confine complementary layers of this type to smallthicknesses, especially less than or equal to 10 nm, especially about 1to 8 nm. Nitrides of a transition metal, such as the nitride of tungstenW, of zirconium Zr, of hafnium Hf, of niobium Nb and of titanium Ti, orelse carbon nitride, may be used. Semiconductor materials, such assilicon, may also be used.

In this case, the materials are chosen depending on their affinity withrespect to glass and/or on the material of the reflective layer and ontheir chemical inertness with respect to the latter. Thus, it may bebeneficial to choose a thin internal layer of Si when the reflectivelayer is made of metal, this material being an effective barrier to thediffusion of alkalis and of oxygen coming from the glass, and also beingable to act as a glass/metal adhesion promoter. The silicon may bedeposited by CVD from SiH₄.

At least one of the complementary layers may also have a chemicalcomposition gradient through its thickness, thereby very advantageouslyenabling two properties to be conferred on a single layer.

This may thus be an "internal" complementary layer based on SiO₂ orSiO_(x) C_(y) becoming gradually richer in silicon, or based on SiO₂ orSiO_(x) C_(y) becoming gradually richer in the oxide of the metal of thereflective layer, such as Al₂ O₃ if the reflective layer is made ofaluminium. The role of promoting adhesion and of reducing mechanicalstresses in the internal layer, with an improved affinity of the latterboth at its interface with the glass and at its interface with thereflective layer, are thus optimized.

The external complementary layer may also have a chemical compositiongradient, based on an oxide of the metal of the reflective layer such asAl₂ O₃, or based on SiO_(x) C_(y), becoming gradually richer in titaniumoxide, the Al₂ O₃ -type oxide having a good affinity and a high chemicalinertness with respect to aluminium when it is this type of materialwhich makes up the reflective layer, the TiO₂ itself being able toimprove the mechanical durability of the stack and possibly to confer onit beneficial anti-misting/anti-fouling properties, as described inPatent FR95/10839 filed on Sep. 15, 1995.

These chemical composition gradients may be obtained by chemical vapourdeposition, by using a distribution nozzle having two injection slots,one for each gaseous precursor necessary for obtaining the twomaterials, and by configuring it so as to cause, along the glass,partial and gradual mixing between the two gas streams emanating fromtwo injection slots, as described, for example, in Patent PCT/FR96/01073filed on Jul. 10, 1996.

The internal and external complementary layers generally have geometricthicknesses of between 1 and 200 nm, especially between 30 and 160 nm ifthey are transparent and between 1 and 5 nm if they are absorbent.

In fact, the thicknesses of the complementary layers are to be modulateddepending on many parameters, including the very nature of these layers,that of the reflective layer and the type of attack to which the stackof layers will be exposed. Thus, it is preferable that the reflectivelayer be chemically "isolated", using both an internal complementarylayer and an external complementary layer, in order to preserve itsproperties during its hot deposition. Furthermore, if the glasssubstrate has thereafter to undergo heat treatments of the annealing,bending or tempering type, these layers will fulfill their protectionrole once again, and in the latter case it may be advantageous to makethem thicker than in the case where the substrate does not have toundergo this type of postdeposition treatment.

Embodiments of the stack of layers according to the invention may be asfollows:

TiN or AlN/Al/AlN

AlN/Al/SiO_(x) C_(y)

Al/SiO_(x) C_(y)

SiO_(x) C_(y) /Al/SiO_(x) C_(y)

Si/Al/SiO_(x) C_(y)

Al₂ O₃ /Al/Al₂ O₃

The invention also specifies the application of a glass substrate, suchas that described previously and the external layer of which is made ofTiO₂ (or ends up as TiO₂ in the case of a layer having a compositiongradient), to the production of an anti-fouling and/or anti-mistingmirror or glazing panel; the same applies to the application of thissubstrate, the external complementary layer of which is harder than thereflective layer and especially based on diamond or on diamond-likecarbon, to the production of anti-abrasion mirrors.

It is also intended for the glass substrate of the invention to beapplied to the production of a heated window, which heats by means of acurrent passing through the reflective layer of suitable thickness.

The subject of the invention is also all the products obtained,especially those obtained after cutting up the ribbon of float glass,preferably using the process defined previously, or by any other processmaking it possible to obtain similar characteristics, especially interms of density and low level (or indeed zero or virtually zero levels)of impurities, especially in the reflective layers.

Two applications are particularly intended: in the first place, theseproducts are intended to be used as glazing panels, both for buildingsand for motor vehicles, the metal reflective layer, especially made ofaluminium, giving these glazing panels a solar protection function. Inthis case, the thickness of the reflective layer is usually limited toat most 30 nm so as to maintain a sufficient level of lighttransmission.

In the second place, they may be used as mirrors. In this case, it isnecessary to achieve a very high light reflectance and this time it istherefore preferable to use metal layers having a thickness of at least30 nm.

More generally, the glass substrate coated according to the inventionhas very diverse applications and can be used in reflecting orsemi-reflecting mirrors, including bottom mirrors in photovoltaic cells,bottom mirrors in basins and mirrors in photocopiers, solar-protectionglazing panels for buildings or any vehicle (of the low-emissivity oranti-solar type), anti-electromagnetic-radiation (radar waves or radiowaves) windows, rear-view mirrors, glass-based furnishing elements, thewalls of a container of aquarium or swimming-pool type, as internalpartitions, and decorative glass. The substrate according to theinvention may also be used by employing the reflective layer as aconducting electrode, for example in electrochemically active glazingpanels, such as electrochromic or "viologenic" glazing panels,liquid-crystal or optical-valve glazing panels.

The invention also relates to the process for manufacturing the stack oflayers with which the glass substrate is coated, especially by hotdeposition of the reflective layer from molten metal powder according tothe "D.P.M." process mentioned previously. The complementary layer orlayers are preferably deposited by chemical vapour deposition or byliquid- or solid-phase pyrolytic deposition.

The preferred method of manufacture consists in depositing all thelayers hot, on the ribbon of a float glass, by preferaby depositing atleast the first two layers in the float-bath chamber. Thus, thedepositions are carried out continuously, making a significant saving interms of time and of production costs compared to techniques in whichthe deposition is carried out in a subsequent step, of the typeincluding sputtering, sol-gel or immersion in a silvering bath, with, inaddition, the solidity and substrate adhesion which are characteristicof layers deposited at high temperature.

One embodiment example of products according to the invention may alsobe a glass substrate, whether a mirror or a glazing panel, whichcontains the sequence:

aluminium/aluminium nitride, or else

aluminium/silicon/oxide, or

aluminium/aluminium nitride.

BRIEF DESCRIPTION OF THE DRAWING

Other details and advantageous characteristics emerge from thedescription below of non-limiting embodiment examples, with the aid ofthe following figures:

FIG. 1: a cross-section of a glass substrate coated according to theinvention;

FIG. 2: a cross-section of that portion of the float-glass chamber inwhich the deposition of the metallic reflective layer according to theinvention is carried out.

It should be pointed out that both FIG. 1 and FIG. 2 are highdiagrammatic representations which do not scrupulously respect theproportions, so as to make them easier to understand.

The following examples were produced on a ribbon of float glass 4 mm inthickness, being a clear soda-lime silica glass which, once cut up, ismarketed by the company SAINT-GOBAIN VITRAGE under the name Planilux.

It could quite equally well be an extra-clear glass or a glass which istinted throughout, such as the glass products which, once cut up, aremarketed by the company SAINT-GOBAIN VITRAGE respectively under the nameDiamant and under the name Parsol.

After cutting, glass substrates are obtained, as shown in FIG. 1, whichare provided with a stack of layers in the following manner: thesubstrate 1 is coated with an optional first layer 2, called interlayer,made of silicon, this interlayer itself being covered by the metalreflective layer 3. The latter is covered by an additional optionallayer 4, once again based on silicon, on which a second additional layer5 is deposited.

In all the examples, the reflective layer 3 is made of aluminium and isdeposited on the glass ribbon by a process explained with the help ofFIG. 2.

The portion of the glass ribbon 10, as shown in this figure, lies withinthe float-bath chamber: the ribbon 10 floats on the surface of a moltentin bath 11 inside a chamber, not shown, containing the tin bath andfilled with a controlled atmosphere composed of a mixture of nitrogenand hydrogen. The glass runs over the tin bath 11 from a glass-meltingfurnace, not shown, lying to the left of FIG. 2, and spreads out thereonin order to form a ribbon which is extracted from the bath at a constantrate in the direction of the arrow by extraction means mounted on theexit side of the bath, on the right-hand side of the figure.

Mounted above the ribbon 10, which has a width of approximately 3.30metres, in a region of the float bath where the glass has acquired itsdimensional stability, is a device 12 arranged entirely inside thefloat-bath chamber. This device is in the form of a gas-distributingnozzle, above the glass ribbon 10, and is arranged transversely to itsrunning axis and over its entire width. The device 12 defines a cavity15 of approximately parallelepipedal shape by means of side internalwalls 14 and an upper internal wall 14', the walls 14 of which,transverse to the glass axis, are substantially vertical or slightlyconvergent or divergent towards the glass. These walls end, at the lowerpart, very close to the surface of the glass, for example at a distanced of less than 20 millimetres from the surface of the glass. Variousopenings are made in these walls:

openings in the upper wall 14' and/or in the side walls 14, providingpassage for the N₂ /H₂ gas mixture in the float-bath chamber inside thecavity 15;

a plurality of openings 16 made in the upper wall 14' or in the upperpart of the walls 14, arranged in line uniformly over the entire widthof the cavity 15, in the manner of injectors, into which emerge inletpipes 17 connected to means for feeding a gas mixture x, these means notbeing shown;

a plurality of openings 18 made in at least one of the transverse sidewalls 14, especially approximately one quarter or 3/4 of the way up thesaid walls, into which emerge gas evacuation pipes connected toextraction means, these not being shown;

a plurality of openings 19 made in at least one of the side walls of thecavity 15, especially in the first third of the height of the cavity,into which emerge gas inlet pipes 20 connected to means for supplying anN₂ /H₂ mixture, not shown, this mixture being similar or identical tothat existing in the float chamber.

Arranged in the thickness of the internal walls 14, 14' and externalwalls 21 of the device 12 are means capable of controlling andregulating the temperature of the cavity 15 over its entire height h,especially lagging/heating means combined with cooling means, theoperation of which is linked to measurements of the temperature insidethe cavity, these measurements being made regularly by suitable sensors:a temperature profile over the entire height h of the cavity is created,either by manual adjustments of the said lagging/cooling means or byelectronic/computer-based automatic control, so as to have a temperaturegradient increasing towards the glass ribbon 10, which starts atapproximately 30 to 100° C. in the upper part near the openings 16 up tomore than 600° C. near the glass.

The device 12 operates in the following manner: vapour from an aluminiumderivative in suspension in an inert gas such as nitrogen (this is themixture x mentioned above) is continuously injected via the openings 16.This derivative may be especially Al (CH₃)₃, Al (C₂ H₅)₃, AlH₃ (NH₃) orAlH₃ (amine). Here it is more specifically dimethylmonoethylamine alane,a hydride stabilized by an amine, decomposing into metallic aluminium atapproximately 180 to 200° C., and the formula of which is AlH₃ (N(C₂H₅)(CH₃) ₂).

In the injection region in the cavity, the temperature is approximately40° C., the mixture x is sprayed into the cavity substantiallyperpendicularly to the plane defined by the glass ribbon 10. Since thetemperature in the cavity increases gradually on moving closer to theglass, the alane decomposes to form pulverulent aluminium 22 in a regionh₁ in the cavity 15 where it reaches its decomposition temperature, thisregion being located approximately in the upper half of the cavity; thealuminium particles are then driven, simply under gravity, into contactwith the glass, while the effluents coming from the decomposition of thealane are extracted via the openings 18, in this powder-forming regionh₁. The parameters of the alane decomposition reaction are adjusted,especially in order to obtain a powder of particles of sufficientlylarge diameter so that it is possible to extract the effluents withoutdriving the powder 22 formed into the extraction pipes and also so as toavoid the effluents reacting at higher temperature with the aluminiumparticles according to an undesired chemical mechanism.

The powder "reaches" the glass ribbon while the latter is at atemperature of from 660 to 700° C., especially approximately 680° C.,that is to say at a temperature which lies between the maximumtemperature at which the glass is dimensionally stable (700-750° C.) andthe melting point of aluminium (approximately 650-660° C.). Thealuminium particles in contact with the glass melt instantaneously andthe droplets coalesce in order to leave a continuous film of moltenaluminium which gradually solidifies as the temperature of the glassdecreases so as to fall below the melting point of aluminium.

The final thickness of the aluminium layer thus deposited may bemodulated as required by adjusting various deposition parameters,especially the alane concentration in the gas mixture x, the flow rateof the said mixture, etc.

Moreover, the H₂ /N₂ gas mixture is injected via the openings 19 so thatthe mixture is sprayed towards the top of the cavity 15, especially in amanner approximately tangential to the side walls 14: in this way, thebuild-up of aluminium powder along its walls is avoided, and thereforethe fouling of the cavity 15 is slowed down, and any risk of a suddenfall of agglomerated particles onto a point on the ribbon, which mayimpair the quality of the coating, is prevented.

Referring to the diagram in FIG. 1, the aluminium layer 3 is thereforedeposited using the device 12 which has just been described. Prior tothis deposition, a thin layer 2 of pure silicon is deposited by CVD, ina known way, from silane, for example as described in French PatentFR-2,382,511, using a nozzle arranged just upsteam of the device 12,when the glass ribbon has already acquired its dimensional stability,that is to say when it is approximately at 700° C.

Before the glass ribbon provided with the silicon interlayer 2 and withthe aluminium reflective layer 3 leaves the float-bath chamber, one ormore additional layers are deposited, the sequences of which will begiven in detail in the following examples. These are aluminium nitridelayers which are deposited by CVD, in a known manner, from aluminiumalkyl or hydride precursors with ammonia or an amine, and/or layers ofan oxide such as silicon oxide or silicon oxycarbide, which aredeposited in a known manner by CVD from silane and ethylene, as isdescribed in Patent EP-0,518,755, or else of tin oxide deposited by CVDin a known manner from gaseous precursors, such as butyltin trichlorideor dibutyltin diacetate, or else of titanium oxide deposited by CVD in aknown manner from gaseous precursors such as a titanium alkoxide of thetitanium-tetraisopropylate type.

It may be noted that instead of, or in combination with, the SnO₂ orTiO₂ oxide layer, it is possible just as well to use silicon oxidelayers deposited by CVD from gaseous precursors such astetraethoxysilane. It would also be possible to use aluminium oxidelayers deposited by CVD from gaseous precursors such as aluminiumacetylacetonate or hexafluoroacetonate. A vanadium oxide layer may alsobe chosen, which may be deposited by CVD from gaseous precursors of thevanadium-alkoxide type such as vanadium tetraethylate, or of the halidetype such as Vcl₅, or of the oxychloride type such as VOCl₃.

Instead of, or in combination with, the aluminium nitride layer, it isalso possible to use a silicon nitride layer which may be obtained byCVD from a gas mixture containing a silane and ammonia and/or an amine.

In the case where it is intended to deposit an oxide layer 5 and not anitride layer above the aluminium layer 3, a thin silicon layer 3,deposited by CVD like the layer 1 previously mentioned, is inserted.

All the depositions are therefore, in the following examples, carriedout in the float chamber, that is to say in a strictly non-oxidizingatmosphere and when the glass is at a temperature falling in stagesbetween approximately 750 and 700° C. for the deposition of the firstsilicon layer and at at least 580-590° C. for the deposition of thefinal layer of the stack, the glass ribbon usually "leaving" thefloat-bath chamber at a temperature of approximately 580° C.

EXAMPLE 1

Using the techniques explained in detail above, the sequence of thefollowing layers is deposited on the surface of the glass ribbon 10 (thegeometrical thicknesses are specified under each of the layers,expressed in nanometres):

    ______________________________________    glass.sup.(1)               /    Al.sup.(3)    /  AlN.sup.(5)    ______________________________________                    50 nm            130 nm    ______________________________________

EXAMPLE 2

The sequence is as follows:

    ______________________________________    glass.sup.(1)               /    Al.sup.(3)  /  (AlN/TiO.sub.2).sup.(5)    ______________________________________                    50 nm          60 nm 50 nm    ______________________________________

EXAMPLE 3

    ______________________________________    glass.sup.(1)           /    Si.sup.(2)                        /  Al.sup.(3)                                  /  Si.sup.(4)                                           /  (SiO .sub.x C.sub.y /TiO.sub.2).                                              sup.(5)    ______________________________________                2 nm       50 nm     4 nm     70 nm 60 nm    ______________________________________

The index of the SiO_(x) C_(y) layer is set here to approximately 1.55.

EXAMPLE 4

This time the sequence is as follows:

    ______________________________________    glass.sup.(1)               /    Al.sup.(3)  /  (AlN/TiO.sub.2).sup.(5)    ______________________________________                    50 nm          60 nm 50 nm    ______________________________________

The index of aluminium nitride is approximately 1.85.

EXAMPLE 5

The sequence is as follows:

    ______________________________________    glass.sup.(1)              /    Al.sup.(3) /  Si.sup.(4)                                        /  SnO.sub.2 .sup.(5)    ______________________________________                   50 nm         4 nm      120 nm    ______________________________________

EXAMPLE 6

The sequence is as follows:

    ______________________________________    glass.sup.(1)           /    Al.sup.(3)                         /  Si.sup.(4)                                  /  (SiO.sub.2 /TiO.sub.2 gradient layer)                                     .sup.(5)    ______________________________________                60 nm       5 nm     120 nm    ______________________________________

The SiO₂ /TiO₂ gradient layer is a layer obtained by CVD and has acomposition containing at least 80% by weight of SiO₂ at the interfacewith the subjacent silicon layer (4) and up to at least 80% by weight ofTiO₂ at the interface with the air. It is obtained according to thetechnique explained in Patent Application FR-95/08421 of Jul. 12, 1995,especially in its Example 9, from the silicon oxide and titanium oxideprecursors mentioned previously.

Next, the glass ribbon in each of these 6 examples is cut up and then oneach of the 6 glass plates the light reflectance R_(L) as a percentageaccording to the D₆₅ illuminant is measured. The following results areobtained:

    ______________________________________           EXAMPLE R.sub.L    ______________________________________           Example 1                   92%           Example 2                   92%           Example 3                   96%           Example 4                   95%           Example 5                   92%           Example 6                   95%    ______________________________________

In conclusion, each of these 6 plates may advantageously be used asso-called "face 1" mirrors, that is to say mirrors where the observerlooks at the glass substrate on the side where it is provided with thereflective layer 3.

It goes without saying that by suitably adapting the sequence of aso-called interlayer 2 and/or additional layers 4, 5, the invention alsomakes it possible to manufacture so-called "face 2" mirrors, that is tosay mirrors in which the observer looks at the substrate on the sideopposite that provided with the reflective layer.

Moreover, the substrates provided with aluminium layers 3 thusmanufactured, but a little thinner, for example from about 10 to 20 nm,may be used as solar protection glazing panels very satisfactorily.

However, it may be seen that it is important to protect as far aspossible the aluminium layer from the risks of oxidation both on line,as soon as it leaves the float-bath chamber, and to preserve it duringoxidizing heat treatments of the bending or tempering type. Theadditional layers 5 according to the invention achieve this effectively.The silicon interlayer 2 is optional; it facilitates the adhesion of thealuminium to the glass and inhibits the reaction which tends to producealumina at the glass/aluminium interface. However, it may be omitted orreplaced by a gas treatment, for example by passing TiCl₄ over thesurface of the glass just before deposition of the aluminium layer.

The silicon layer 4 above the aluminium is also optional; it makes itpossible to guarantee that the aluminium layer does not oxidize duringdeposition of the next oxide layer.

For optical reasons, especially in order to increase the lightreflectance, it is also possible to deposit additional layers,especially oxide layers, on the other face of the glass ribbon, forexample in a subsequent step.

The invention has therefore developed the continuous manufacture ofmirrors or of solar-protection glazing panels, on the float line, whichmanufacture is highly advantageous in terms of both yield and cost. Thealuminium layer thus deposited is of high quality and is especially verydense, very pure and particularly adherent to the glass (or to the layerwhich is subjacent to it).

We claim:
 1. A process, comprising:depositing a metallic reflectivelayer on a surface of a ribbon of float glass by contacting the surfaceof the float glass with a pulverulent metal or molten metal in an inertor reducing atmosphere, wherein the metal has a melting point that isless than or equal to the temperature at which the ribbon acquiresdimensional stability, and wherein the ribbon temperature during thecontacting is such that the pulverulent metal melts and coalesces at thesurface of the ribbon or the molten metal forms a sheet at the surfaceof the ribbon to provide a solid continuous metallic reflecting layerwhen the ribbon temperature is less than or equal to the melting pointof the metal.
 2. Process according to claim 1, characterized in that the"metal" is based on a single metal, or based on an intermetalliccompound, a metal alloy or a eutectic compound.
 3. Process according toclaim 1 or claim 2, characterized in that the "metal" is based on atleast one of the metals belonging to the group comprising aluminium,zinc, tin, cadmium and, optionally, comprises silicon.
 4. Processaccording to one of the preceding claims, characterized in that thedeposition is carried out in the float-bath chamber.
 5. Processaccording to claim 1, characterized in that the deposition is carriedout downstream of the float-bath chamber, especially in an essentiallysealed box optionally extending the said chamber.
 6. Process accordingto one of the preceding claims, characterized in that the deposition iscarried out when the glass is at a temperature greater than or equal tothe melting point of the metal.
 7. Process according to claim 6,characterized in that the contacting of the metal in pulverulent formwith the surface of the glass takes place by spraying a powder insuspension in a carrier gas, this being inert or reducing, especiallyusing a distribution nozzle arranged above the glass ribbon andtransversely to its running axis, and capable of distributing the powderover the entire width of the ribbon.
 8. Process according to claim 7,characterized in that a powder particle size of between 0.1 and 100 μm,especially between 1.0 and 50 μm, is chosen.
 9. Process according toclaim 4, characterized in that the metal is generated in pulverulentform (22) above the glass ribbon, from metal derivatives, especiallygaseous ones, the decomposition of which into metal is brought about bythermal activation and/or bringing them into contact with each other.10. Process according to claim 9, characterized in that the derivativesare chosen from metal alkyls, metal hydrides, mixed metal hydride/metalalkyl compounds complexed by ammonia or by a primary, secondary ortertiary amine.
 11. Process according to claim 9 or 10, characterized inthat the derivatives decompose into metal at a temperature of between50° C. and 600° C., especially between 100° C. and 450° C.
 12. Processaccording to one of claims 9 to 11, characterized in that at least oneadditive which promotes nucleation or growth of the metal particles isassociated with the metal derivative(s).
 13. Process according to one ofclaims 9 to 12, characterized in that the metal derivative(s) areintroduced above the glass ribbon (10) in gaseous form using a device(12) comprising a cavity (15) whose walls (14, 14') define a channel forguiding the powder (22) generated by the said derivatives towards theglass ribbon (10).
 14. Process according to claim 13, characterized inthat the walls (14) of the cavity (15) are substantially vertical,possibly convergent or divergent towards the glass ribbon (10), and inthat a thermal gradient is created over at least part of the height (h)of the said cavity.
 15. Process according to either of claims 13 and 14,characterized in that the metal derivative(s) are injected in the upperpart (16) of the cavity (15) and in that the effluents arising from thedecomposition of the derivatives are extracted by side evacuation means(23) made in the walls (14) of the said cavity (15), preferably at thelevel, or near the level, where the metal powder is formed and where itreaches a sufficient particle size.
 16. Process according to one ofclaims 13 to 15, characterized in that an inert or reducing gas isinjected at at least one point (19) in the cavity (15).
 17. Processaccording to one of claims 7 to 16, characterized in that the metalpowder liquefies on the glass ribbon (10) or in the vicinity of it. 18.Process according to claim 1, characterized in that the molten metal issprayed towards the glass ribbon, especially using a static distributingnozzle delivering a curtain of molten metal above the ribbon andtransversely to its running axis, or using a moving nozzle, given ato-and-fro movement transverse to the running axis of the ribbon. 19.Process according to one of the preceding claims, characterized in thatthe surface of the glass ribbon is treated before depositing themetal-based reflective layer (3), especially by a contacting/adsorptionof vapour of the TiCl₄ type, or by depositing at least one interlayer,especially made of silicon Si, made of an oxide such as aluminium oxideAl₂ O₃, silicon oxide, oxynitride or oxycarbide, SiO₂, SiON or SiOC,zirconium oxide ZrO₂, cerium oxide, titanium oxide TiO₂, zinc oxide ZnO,or boron oxide, yttrium oxide, magnesium oxide, or a mixed oxide of Aland of Si, made of fluorinated aluminium oxide, of magnesium fluoride orof a nitride such as aluminium nitride AlN, silicon nitride Si₃ N₄,titanium nitride, zirconium nitride, or a carbide, which layer isdeposited, for example, by chemical vapour deposition.
 20. Processaccording to one of the preceding claims, characterized in that themetal-based reflective layer (3) is covered with at least one additionallayer (5) intended to protect it from oxidation, especially when theglass ribbon is still in the inert and/or reducing controlled atmospherein which the deposition of the said reflective layer was carried out.21. Process according to claim 19, characterized in that the additionallayer(s) chosen is (are) based on a nitride, such as aluminium nitride,silicon nitride or titanium nitride.
 22. Process according to claim 19or 20, characterized in that the additional layer(s) chosen, optionallydeposited on a thin silicon "sacrificial" layer (4), is (are) based onan oxide(s) comprising at least one oxide of the following group:titanium oxide TiO₂, tin oxide SnO₂, zirconium oxide ZrO₂, siliconoxide, oxycarbide and/or oxynitride SiO₂, SiOC or SiON, aluminium oxideAl₂ O₃, vanadium oxide, zinc oxide, niobium oxide, tungsten oxide,antimony oxide, bismuth oxide, tantalum oxide or yttrium oxide, made ofaluminium nitride or silicon nitride, or of fluorinated tin oxide ormade of carbon-like diamond.
 23. Process according to claim 19 or 20,characterized in that the reflective layer (3) is covered with anadditional layer (5) having a composition gradient or a refractive indexgradient through its thickness, especially by depositing a material suchas silicon oxide, which becomes gradually richer in a material such astitanium oxide.
 24. Process according to claims 19, characterized inthat the reflective layer (3) is covered with at least one sequence oflow-index and high-index layers, for example a SiO₂ /TiO₂ sequence. 25.Process according to one of the preceding claims, characterized in thatthe glass ribbon of a float line is substituted either by a glass ribbonnot coming from a float line or a non-continuous glass substrate, suchas a glass plate.
 26. Glazing panel (1) obtained by cutting up thefloat-glass ribbon (10) covered according to the process in accordancewith one of the preceding claims, characterized in that it is providedwith an aluminium reflective layer (3) having a thickness less than orequal to 30 nm, depending on the solar protection.
 27. Mirror (1)obtained by cutting up the float ribbon (10) covered according to theprocess in accordance with one of the preceding claims, characterized inthat it is provided with an aluminium reflective layer (3) having athickness greater than or equal to 30 nm.
 28. Glazing panel (1)according to claim 26 or mirror according to claim 26, characterized inthat it is provided with the aluminium/SiOC or aluminium/AlN oraluminium/TiN or aluminium/Si/oxide sequence.
 29. Glass substrateprovided with at least one reflective layer (3) based on a metal of theintermetallic-compound, alloy or eutectic compound type, especiallybased on at least one of the metals belonging to the group comprisingaluminium, zinc, tin and cadmium and, optionally, also comprisingsilicon, characterized in that the substrate (1) is also provided withan "external" complementary layer (4) and/or with an internalcomplementary layer (2), with respect to the said reflective layer (3),the complementary layer(s) being intended to ensure its chemical and/ormechanical durability.
 30. Glass substrate (1) according to claim 29,characterized in that the "internal" complementary layer (2) and/or the"external" complementary layer (4) are based on material(s) whichis(are) transparent in the wavelengths lying within the visible and ofthe oxide(s) type chosen from at least one of the compounds comprisingthe oxides, oxycarbides or oxynitrides of the elements in Group IIA,IIIB, IVB, IIIA and IVA and of the lanthanides in the Periodic Table,such as the oxides of Mg, Ca, Y, Ti, Zr, Hf, Ce, Al, Si, Sn, or elsebased on transparent doped metal oxides such as F:SnO₂.
 31. Glasssubstrate (1) according to either of claims 29 and 30, characterized inthat the "internal" complementary layer (2) and/or the "external"complementary layer (4) are based on material(s) which is(are)transparent in the wavelengths lying within the visible and of thenitride(s) type, especially based on a nitride of at least one of theelements in Group IIIA in the Periodic Table, such as the nitride of Al,of Ga or of boron, or else based on silicon nitride.
 32. Glass substrate(1) according to claim 28, characterized in that the "internal"complementary layer (2) and/or the "external" complementary layer (4)are based on material(s) which is(are) transparent within thewavelengths lying within the visible and of the carbon-like-diamondtype.
 33. Glass substrate (1) according to claim 29, characterized inthat the "internal" complementary layer (2) and/or the "external"complementary layer (4) are based on material(s) which is(are) absorbentin wavelengths lying within the visible and are different from those ofwhich the reflective layer (3) is composed, of the transition-metalnitride type, such as the nitride of W, of Zr, of Hf, of Nb or of Ti, orcarbon nitride, or else made of silicon Si, these preferably beingconfined to geometric thicknesses of less than or equal to 10 nm,especially of about 1 to 8 nm.
 34. Glass substrate (1) according toclaim 29, characterized in that the "internal" complementary layer (2)and/or the "external" complementary layer (4) has a chemical compositiongradient through its thickness, especially an "internal" complementarylayer (2) based on SiO₂ or SIO_(x) C_(y) becoming gradually richer insilicon, or based on SiO₂ or SiO_(x) C_(y) becoming gradually richer inAl₂ O₃, and/or an "external" complementary layer (4) based on Al₂ O₃ orSiO_(x) C_(y) or SiO₂ becoming gradually richer in TiO₂, or based on Sibecoming gradually richer in SiO_(x) C_(y) or in SiO₂.
 35. Glasssubstrate (1) according to claim 29, characterized in that the geometricthickness of the "internal" complementary layer (2) and the "external"complementary layer (4) is between 1 and 200 nm, especially between 30and 160 nm.
 36. Glass substrate (1) according to one of claims 29 to 35,characterized in that the reflective layer (3) lies between an"internal" complementary layer (2) and an "external" complementary layer(4), the nature and thickness of which are chosen so as to preserve theproperties of the reflective layer (3) during its hot deposition and,optionally subsequently in the case where the glass substrate (1) isintended to undergo, after deposition of the layers, a heatpost-treatment of the annealing, bending or tempering type.
 37. Glasssubstrate according to one of claims 29 to 36, characterized in that thereflective layer (3) has a density at least than 80 and especially of atleast 90 or 95% of its theoretical density.
 38. Glass substrateaccording to one of claims 29 to 37, characterized in that thereflective layer (3) has a level of impurities, especially C, N, O, ofat most 3 at. %, especially of at most 1 at. %.